Centro-asymmetric optical fibers are those fibers having an asymmetric cross-section. Typically, asymmetric optical fibers include those that have one side of the optical fiber located near the optical guiding region, or core. The non-circular cross-section of the outer surface of such a fiber may have a predetermined geometric relationship to the transverse axes of the guiding regions, so that the orientation of those axes can easily be ascertained from the geometry of the outer, e.g flat, surface of the fiber. For example, the axes of birefringence are positioned by locating the flat of the asymmetric fiber against a flat surface or by examining the reflection from the flat, thus locating the birefringence axis no matter how far down the fiber from the reference point. Easily locating the birefringence axis on the asymmetric fiber allows low cost polarization maintaining fusion splicing to other asymmetric fibers, e.g. those fibers with a D-shaped cross-section, using e.g. industry standard fusion splicers. In contrast, circular clad polarization maintaining fibers that have a degree of internal twist lack such angular reference, making them difficult to splice without losing polarization maintaining performance.
Circular clad polarization maintaining fiber can be used in fiber optic gyroscope (FOG) sensing coils. For example, circular clad fibers may provide enhanced polarization maintaining performance and/or may have a thin coating allowing for more optical fiber in the FOG. A FOG with a higher coil volume may increase sensitivity and improve FOG performance.
However, asymmetric, e.g. D-shaped fiber can be used in e.g. other FOG components and other devices, e.g. voltage controlled attenuators, tunable filters, phase modulators, amplitude modulators, optical intensity limiters and polarization controllers. While it may be useful to splice such asymmetric fiber to circular clad fiber, dissimilar fiber optic cross-sections are difficult to splice together. For example, large transverse movements or offsets with respect to the optical mode field size between the two dissimilar fibers may be present due to, for example, asymmetrical forces from surface tension during the fusion molten glass stage. Further, even if tolerable insertion loss is achieved, such a fusion splice may be weak due to, for example, high stresses at the junction between dissimilar cross-sections.
As a result, there is a need for a method that effectively splices circular clad fiber to asymmetric fiber, and results in a fiber optic composite with high strength and low loss properties.